This section provides background information related to the present disclosure which is not necessarily prior art.
More than 500,000 patients underwent total knee replacement (TKA) in 2012 in the United States alone, a number that is expected to exceed three million by the year 2025. The rehabilitation process for TKA patients is extensive, costly, and does not always yield optimal results. Many patients struggle to re-gain full mobility following TKA because stiffness in the knee joint can quickly progress to scar tissue in a short time. If this process is not prevented, scar tissue may impede flexibility in the future. Lack of full range of motion not only affects gait and mobility, but can also lead to future back, hip, and joint pain.
The process of inhibited flexibility and accumulation of fluid following TKA progresses through four stages: bleeding, edema, granulation tissue, and fibrosis. Cytokines in the inflammatory cells draw in fibroblasts, which begin to lay down collagen tissue. As the collagen hardens it becomes more and more difficult to eliminate. Scar tissue is basically all collagen and will eventually become fibrosis. This progression typically begins soon after surgery and is well on its way to permanently impeding mobility within 2-4 weeks when outpatient physical therapy typically begins. Lack of range of motion is not normally a focus during the first few weeks of therapy. By the time outpatient physical therapy begins (on average 3-4 weeks post-TKA), it is often not possible to prevent and treat the accumulation of fluid in the periarticular tissue. Failure to achieve a full range of motion in the immediate or early postoperative period, combined with permitting the accumulation of even relatively small amounts of periarticular blood and edema, naturally permits extracellular matrix and collagenous scar tissue to be deposited, such that full range of motion may never be fully recovered. A device and method for removing fluid containing fibroblasts from the periarticular tissue before collagen begins to form would therefore be desirable.
Patients and therapists often resist early rehabilitation because they believe that early manipulation of the joint is exceedingly painful. By limiting the force or pressure used to move a patient's joint to below the patient's comfort threshold, it is possible to decrease or eliminate pain while focusing on terminal extension and flexion.
Patients and physical therapists often delay range of motion therapy after TKA because patients typically experience too much pain if the leg is manipulated toward full range of motion soon after surgery. Existing methods for treating a lack of range of motion include manually pushing and pulling just above and below the knee by a trained physical therapist in an effort to gain better extension and flexion. If the pressure applied is overdone, a risk of doing more damage exists and the inflammatory cycle that started the problem may be repeated. On the other hand, too little pressure results in insufficient progress.
Another issue with existing TKA rehabilitation procedures is that not all patients are the same in terms of their response to therapy. Some patients tend to form scar tissue more rapidly, thicker, and more densely than others. Patients that develop hypertrophic scar and keloids will exhibit loss of function at a faster pace than normal.
Continuous passive motion machines (CPM) are often used in existing TKA therapies. CPM machines depend on flexion and extension values to determine motion. CPM machines push blindly and have no pressure feedback and no pressure variability. CPM machines also cannot stop in mid-cycle, such as to allow for fluid to exit the joint. CPM machines further are not able to provide a high or low amplitude stretch at the extremes of the patient's range of motion, such as by holding the leg in a flexed or extended position. It would therefore be desirable to provide a device and method capable of increasing a patient's range of motion more quickly while minimizing pain.
CPM machines undesirably set limits on extension and flexion and operate only within these limits. If the limits are set too aggressively, the joint can experience excess stress, leading to pain and potentially additional injury. Typically, CPM machines are used to exercise a pre-specified range of motion limited by fixing the target angles within the patient's existing range of motion, which is already achievable by the patient. This becomes self-limiting and can undesirably leave periarticular fluid in the joint, reinforcing existing limits of extension and flexion, and preventing meaningful progress.